The purpose is to investigate the neurobiological factors that affect craving for nicotine, direct effects of nicotine on mood and behavior, and nicotine self-administration. We will examine how these measures are affected by acute doses of dopaminergic drugs (i.e. bupropion, bromocriptine, d-amphetamine, and haloperidol). We hypothesize that the direct and indirect dopamine agonists will produce effects that are opposite to the dopamine antagonists.